Recently, gallium nitride (GaN)-based white light emitting diode (LED) is actively developed and manufactured throughout the world. In such a GaN-based white LED, blue, green, and red LED chips are simultaneously lightened and then the brightness of the LED chips is adjusted such that variable coloring mixing can be achieved, thereby expressing a white color, or blue and yellow (or orange) LED chips are simultaneously lightened while adjusting the brightness thereof.
However, in the above two multiple chip-type white LED manufacturing methods, the LED chips have different operational voltages, and color coordinates are changed depending on the output of the LED chips which may be vary according to the ambient temperature.
As another method, phosphor may be coated on a blue or a near-UV (ultra violet) LED chip to fabricate a white LED.
In the above method for manufacturing the white LED by coating phosphor, the manufacturing process is more simple and economical, and a light source having a desired color is more simply manufactured through the variable color mixing of three colors using blue, green, and red phosphor, as compared with that of the multiple chip-type white LED manufacturing methods. However, in the phosphor coating method, the primary light emitted from a light emitting device is changed into the secondary light through phosphor, so that the light source using phosphor may have brightness, a correlated color temperature (CCT), and a color rendering index (CRI) varied according to the performance and the application scheme of the phosphor.
Recently, most white LEDs have been manufactured according to the combination of (In)GaN LEDs emitting blue light having a wavelength of about 460 nm and yttrium aluminum garnet (YAG) Ce3+ phosphor emitting yellow light.
However, since conventional the (In)GaN LEDs emits blue excitation light having a narrow band, the development of light emitting devices expressing various colors is difficult, and white light may be seriously changed according to the wavelength of blue light. In addition, light emitting efficiency may be excessively lowered in UV excitation light.